docs: def get_index(lis, argument):
      """Find the index of an item, given either the item or index as an argument.
  
      Particularly useful as a wrapper for arguments like channel or axis.
  
      Parameters
      ----------
      lis : list
          List to parse.
      argument : int or object
          Argument.
  
      Returns
      -------
      int
          Index of chosen object.
      """
      # get channel
      if isinstance(argument, int):
          if -len(lis) <= argument < len(lis):
              return argument
          else:
              raise IndexError("index {0} incompatible with length {1}".format(argument, len(lis)))
      else:
          return lis.index(argument)